301 Maxwell Lecture: Bacillus probiotics in nursery pigs: The effects of dose on gut health and performance

Weaning is one of the most stressful events in the life of a pig and critical for their health and development. To reduce the use of antibiotics and zinc oxide in nursery diets, many feed additives have been tested to demonstrate their efficacy in weaning pigs. Bacillus subtilis, a heat-resistant spore-forming bacteria, consumes oxygen in the digestive tract and can provide a favorable anaerobic environment for lactic acid-producing bacteria, resulting in their proliferation. It also produces several digestive enzymes, such as amylase, protease, and antioxidant enzymes. In addition, Bacillus species are known to alter the gut microbiome and increase the production of short-chain fatty acids in the gut. Therefore, Bacillus probiotics have been widely used in nursery diets to effectively improve growth performance and protect piglets from weaning stress and postweaning diarrhea. However, when the probiotics are supplemented in diets for weaning pigs, their efficacy is dependent on multiple factors, such as strains, the health condition of the animals, product composition, and the dose of the probiotics. There has been tremendous effort in establishing the optimal supplementation level of probiotics for nursery pigs to maximize the efficacy of their supplementation, but a high dose of probiotics could be detrimental to the gut health and microflora of nursery pigs, as it could increase the incidence of diarrhea and may have potential side effects in the immune system, antibiotic resistance, and the production of unfavorable metabolites in the gut. A study was conducted to demonstrate the effect of Bacillus probiotic supplementation for nursery pigs at the recommended and high doses (10 times greater bacterial counts than the recommended dose) compared with a control treatment with no probiotic supplementation. In the study, the Bacillus supplementation at the recommended dose did improve the early postweaning growth rate, increase the production of fecal short-chain fatty acids (acetate, propionate, and butyrate), and blood glucose concentrations, and alter the fecal microbiome. However, high-dosing probiotics in nursery diets did not show any beneficial effects that were shown in the pigs fed diets with Bacillus probiotics at the recommended dose. Bacillus-probiotic supplementation in nursery diets may enhance growth performance and benefit gut health, but a high dose of probiotics does not always lead to comparable positive effects for pigs. Therefore, it i